Methods and apparatus for preparing a hemispherical surface

ABSTRACT

Methods and apparatus for preparing at least a hemispherical surface with a desired dimension have been disclosed. The method includes at least two steps: a primary cutting mode for mostly reaming a lower portion of the target site, which enveloped area from the pole to intermediate latitude and a finishing cutting mode for reaming either an upper portion or an entire area of the site by less number of times of rotation, respectively. The intermediate latitude locates between the pole and the equator of hemisphere.

FIELD OF INVENTION

The present invention relates to methods and apparatus for preparing at least a hemispherical surface with a desired dimension in separated, partially cutting steps. In particular, the invention relates to procedure of preparing the acetabulum cavity in surgery of the hip replacement and other field beyond the medical.

DESCRIPTION OF THE PRIOR ART

A process of cutting a full or partial hemispherical surface by a single dimension rotation tool (like a lathe) always meets a problem of zero or a lower cutting speed at pole area or nearby of the sphere. In medical field, a process of reaming the defected acetabulum in surgery of the hip replacement has met a same problem and should always be considered as a critical challenge to the overall outcome of implanting the prosthesis from many respects of concern. If directly using the identical size of the dome-like reamer reams the cavity, the larger difference of the cutting rate between the pole and equator point will cause a significant excess cutting in equator area, but not or less cutting in polar area.

From practical experiences, smaller reamer used, easier to ream the apex area of the cavity, due to the small difference of cutting rate from point of the apex point to equator. In order to reduce the uneven cutting problem, acetabular reamers used in the prior art generally include using a series set of reusable, hemispherical dome-like reamer with a progressive increment on diameter. An interval of the diameter between adjacent reamers is about 2 mm. The procedure of reaming the defected acetabulum always starts from a smaller size of reamer, such as a size is similar as or smaller than one of the existing cavity, or at least two sizes smaller than the size of preoperatively selected acetabular prosthesis. The smaller reamer used is more convenient for reaming the area near the pole by swinging the shaft handle away from the longitude axis of the sphere with less damage on the upper portion of hemisphere. Then surgeon step by step interchanges a next reamer with a larger size of reamer to enlarge the diameter of the cavity until reaching a desired size. Reaming hemisphere by progressive reamers somehow is reluctance, but no ideal choice, particularly, for robot system.

In general, reaming the defected hemispherical acetabulum normally needs step by step interchanging at least 3-5 serials reamers. It is conceivable that each operation step must be very carefully carried out, in term of repeatedly positioning reamer in same direction of the spherical axis and controlling a proper depth cut by each reamer, as well as avoiding tissue damages during inserting and removing the reamer from incision site. In the case of manually operating the reamer, in which there is such a small opening of incision and a limited, direct sight view, it is a kind of challenge for surgeon's experience and skill. Otherwise, missing the direction of the axis of the hemisphere and improperly controlling a depth cut of the cavity to correspond to the size of each reamer used will cause variation of the dimension, surface and orientation of the cavity cut. Obviously, it is unavoidable during reaming with repeatedly interchanging the reamer, even surgeon has a help from CAOS. From the point of view of clinic, a solution for overcoming these problems through either the improved method for or the better apparatus used in reaming acetabulum, or both are strongly desired.

Furthermore, now the navigation and robotic technologies (CAOS) become more and more popular in hip replacement surgery because of their potentials on filling unmet needs in a respect of the total surgical quality and its long term results of operation. However, because of outdated procedure currently associated with robotic system, particularly, frequently interchanging reamer heads during reaming, until now, surgeons seem not fully see facts of that robot performances performs as well as or better than one human does, in term of skillful and flexible yet. It becomes a major hurtle of widely promoting the robot system into hip replacement surgery. So in order to explore overall functions and more advantages of the robot in surgery, the market needs is far beyond how good the robot is, but how well the state of the art of surgical technologies can associate with the robot system in term of tooling, prosthesis design and procedures of the hip replacement. In particular, it is desirable a method that there are few steps of or without exchanging reamer head during reaming and a better accuracy of the spherical surface.

SUMMARY OF THE INVENTION

The present invention here dedicates suitable apparatus and cutting methods for respectively reaming section of the hemispherical surface in various steps. In general, it includes successive steps of: a primary cutting mode for reaming the lower (first) portion of the target site, typically dedicated as Zone A of a hemisphere, in FIG. 1 and a finishing (or secondary) cutting mode either for reaming upper (or second) portion of the target site, typically dedicated as Zone B of a hemisphere, in FIG. 1, or for reaming entire area of the hemisphere.

As first advantage, the method could possibly generate a hemisphere by using only two reamers or by a single reamer, which can precisely execute both cutting modes, without steps of frequently interchanging the reamer head as did in conventional procedure in hip replacement surgery and scarifying the quality of the cavity reamed.

As second advantage, the apparatus suitable for the method in the present invention could be in various designs in order to be applicable for various status or type of the operation, such as MIS, resurfacing and revision of the hip replacement surgery.

As other advantage, any available principle/techniques for cutting hemisphere, such as any types of cutting element used, are suitable to be adopt on the reamer design in the present invention, such as the conventional thin-wall hemispherical dome reamer and others disclosed in the prior art.

As another advantage, a design of reamer includes a limited number of parts. So, it can consistently and reliably move between the first and second positions. Further, the reamer can be made in a less expensive and disposable format.

As a further advantage, once the method for cutting hemisphere applied in the clinical, it will save a lot of the operation time, correct some mistakes related to humanity factors and provide higher accurate and quality acetabular cavity in many respects.

As addition advantage, an acetabular reamer in the present invention can appeal to a wide range of orthopedic surgeons with various skills and experience. Further yet, the training and skill level required to use the method and reamer and become proficient with it is not overly taxing on the orthopedic surgeon.

Further yet, the cutting method and apparatus for reaming a hemispherical surface are fully compatible with manual and various navigation and robotic systems used in hip replacement surgery, which are able to explore overall capabilities and advantages of how performed and results of the surgical robot exceeding human's ability.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1. The radial radius variation (Δr) between adjacent layers v. s. a depth of the hemisphere. Two cutting zones divided by radius variation.

FIG. 2. A first preferred structure of an adjustable reamer has a lower and an upper cutting surface configured by a cutting element of a thin-wall dome, which are arranged and switchable along the longitude axis of the hemisphere.

FIG. 3. A second preferred structure of an adjustable reamer has a lower configured by a cutting element of offset circular blade and an upper cutting surface (a type of thin-wall dome as a cutting element), which are arranged along the longitude axis of the hemisphere and collapse-able.

FIG. 4. A flow chart of a reaming method (steps) corresponds to the first and second preferred embodiment of apparatus.

FIG. 5 a. An alternative structure of an adjustable reamer has a retractable upper cutting surface configured by offset circular blade as a cutting element.

FIG. 5 b. An alternative structure of an adjustable reamer has a swing-able upper cutting surface configured by offset circular blade as a cutting element.

FIG. 6. A flow chart of a reaming method corresponds to the third and fourth preferred embodiment of apparatus.

FIG. 7. A flow chart of a reaming method corresponds to the fifth preferred embodiment of apparatus.

FIG. 8. A structure of a reamer with a lower and an upper cutting surface configured by a cutting element of thin-wall dome, which are able to simultaneously rotate in different speed along the longitude axis of the hemisphere.

SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus, method, and steps of the present invention are now described in more detail. Some of these details described in the method and apparatus are known to those skilled in the art and will not be discussed in great detail. Further, one skilled in the art will appreciate that certain steps may be altered or omitted while other steps may be added without departing from the scope of the invention. The novel method and apparatus of the present invention, for example, can be applied to surgery of hip arthroplasty, to revision surgeries for total and partial hip replacement, as well as to other fields beyond the orthopedic surgeries and the medical field.

The Principle of the Method:

Any hemisphere with a desired dimension can be imagined as one stacked up a plurality of circular rings with a progressive increased radius (r_(i)) along the polar axis of the hemisphere. FIG. 1 has shown: X axis is a depth (D) or radius (R) of the hemisphere and Y axis is the difference of the horizontal radius between adjacent rings, marked as Δr_(i)=r_(i)−r_(i-1), defining as the horizontal distance from a point on the hemispherical surface to the axis of the hemisphere. The location of each ring (i) here correspond a specific depth or a height hemisphere. The increment of interval of depth is about 1 mm along the polar axis of the hemisphere. The dot line curve here represents data from a hemisphere with a radius (R) of 30 mm and solid line curve does one with the radius of 22 mm.

The curve in FIG. 1 has explored a typical uneven change rate, Δr_(i), corresponding to each circle radius of the ring (i). For one dimension cutting mode, a linear cutting speed (called a cutting speed) applied at each point of hemispherical surface is solely proportion to the horizontal radius (r_(i)) of each layer (the ring). So at the pole point, the radius and the cutting speed all are zero. At the equator, the radius and the cutting speed all reach to maximum, regardless the radius of the sphere. As the principle used in CNC machine, that different speed applied on the corresponding point of sphere would bring a uniform cutting effect at each point. In other word, the final linear cutting effect at each point of the sphere can be compensated by continuously varying turning speed. Of course, more speed zone applied, better or more uniform cutting effect had. In reality, the curve in FIG. 1 could be divided into at least two zones: 1) a zone A having a sharply increasing speed of cutting with the depth, which represents area from the pole to intermediate latitude in left side of FIG. 1 and 2) a zone B having a slow/flat increasing speed of cutting with the depth, which represents area from the intermediate latitude to the equator in the right side of FIG. 1. A position of the intermediate varies little with the radius of the sphere.

In the zone A, the linear cutting rate is rapidly decreasing while the depth approaches to near zero. In opposite, in zone B, it changes a little while the depth approaches to equator. Such the phenomena lead two conclusions: 1) there is no way to ream a perfect hemisphere by one dimensional rotation of cutting or solo or even cutting speed, because significant difference of the cutting speed distributed through the overall cutting area. 2) various cutting frequency or number of times of rotation applied at different radius zone would somehow compensate such the influence of uneven cutting.

In other word, the effects of the circle radius difference, Δr, could be compensated by either a specific total number of cutting times or cutting frequency applying on each point or latitude. For example, the cutting effect of a higher cutting frequency applied at area with smaller circle radius, r_(i), (near the pole) could perform same as or close to one of a lower cutting frequency applied at area (near equator) with larger circle radius. By same token, any method or apparatus which can reduce or postpone the cutting efficiency acted on area with a larger circle radius, r_(i) (in a upper cutting layer) of the hemisphere also gives behaviors similar as an effect of the cutting frequency compensation (CFC), when the reamer is rotated by even cutting speed. But in reality, multiple cutting speeds applied might be too complicate to design a device. To particularly extending such the idea of CFC, one could define it into at least two cutting speed zones or equivalent, such as a primary cutting mode for cutting lower portion of the target site (the bottom area near pole of the hemisphere (zone A)) and a finishing mode either for reaming upper portion of the target site, typically dedicated as Zone B of a hemisphere, in FIG. 1, or for reaming entire area of the hemisphere (including zone A and zone B together) after accomplishing the primary mode. The method or procedure could be applied in either simultaneous or successive cutting modes on each zone area by either different cutting frequencies or different number of cutting times. A typical successive example is first partially reaming or no reaming the upper portion, while fully reaming the lower portion of the site in the primary mode, then reaming both zones together until reaching a full continuous hemispherical surface.

According to the principle described above, any types of the cutting element equipped in the reamer disclosed in the prior art should be used for and be suitable for designing apparatus and implementing the method, if cutting element used can present a dynamic spherical cutting profile in a partial or full hemispherical form, while it is rotated around the longitude axis. For instance, such as a thin shell dome-like reamer with a cutting teeth in conventional reamer, a semi-circular blade as disclosed in U.S. Pat. No. 5,755,719 by Frieze, in which semi-circular blade has a same radius of the curvature as spherical one of the cutting target and rotates around the polar axis of the hemisphere, or a circular blade(s) as a cutting element is positioned in a manner of that its turning axis diverges from the longitude axis of the hemisphere by certain angle as disclosed in publication of US 20100076442 by Xie, all could be candidate.

The typical zone A here represents area from the pole to intermediate latitude. The intermediate latitude is located between the pole and the equator of the hemisphere. The zone B represents area from the intermediate latitude to the equator of the hemisphere. The boundary line (or intermediate latitude) between two zones approximately locates at a range of 35-55 degree latitude of hemisphere (here the pole=90 degree latitude) and varied with the radius of the sphere to be cut. The more preferred intermediate latitude is at 45 degree latitude.

The present invention here dedicates a cutting method for preparing a full continuous hemispherical surface, which includes both concave and convex surface.

Particularly, the method primarily dedicates successive steps including: respectively reaming bottom (first) and upper (second) portions of the hemispherical surface in separated steps. For instance, a primary cutting mode for mostly reaming the lower latitude area or the bottom portion of the hemisphere, typically dedicated as Zone A in FIG. 1, in order to generate a partial hemisphere with a desired dimension and a finishing (secondary) cutting mode either for reaming upper portion of the target site, typically dedicated as Zone B of a hemisphere, in FIG. 1, or for reaming entire area (Zone A and Zone B together) of the hemisphere after accomplishing the primary mode. Of course, an apparatus having more than two layers of cutting surface could also be option for completing the process above.

As discussed, the method is directly related to a method of separately or step by step cutting each specific area of the hemisphere, which is quite different from serially cutting same area by frequently interchanging the reamer head with a increasing size in the conventional procedure. A single or at most two reamers having identical spherical cutting radius can complete reaming the cavity with a desired size, quality and a shape, which significantly simplifies the procedure of reaming and avoids many unnecessary steps and mistakes as realized.

In the primary mode, as one option, the surgeon firstly rotates the reamer with the lower cutting surface (covering Zone A) for fully reaming a bottom portion of the target site. The lower cutting surface could be either a primary reamer having a fixed, partial dynamic hemispherical cutting surface or an adjustable reamer in the first position with a first shape. The adjustable reamer comprises at least a lower and upper cutting surface, but in the primary cutting mode, the upper one is not in working position or is not fully functioning. The lower cutting surface in both reamer has a desired spherical radius and has dynamically enveloped the area from pole to intermediate latitude of the hemisphere (presented the zone A), in order to at least form the partial hemisphere in the bottom portion. At this mode, surgeon could implement enough number of times of rotation on the area near the pole without worrying overcutting other sections above.

In the finishing mode, surgeon uses either the adjustable reamer having a second shape while it is in second position (both cutting surfaces are in working position) or a finishing reamer with a fixed, full continuous dynamic hemispherical cutting surface, like a regular dome-like acetabular reamer to ream entire area of the site to reaming entire area of the site. Both cutting surfaces in the reamer have a desired spherical radius and are same as one of the lower cutting surface. This step takes less time and effort on enlarging the upper section of the hemisphere as well smoothing entire surface because of a higher efficiency of the full size reamer used as discussed. In other word, total number of cutting times applied in the primary mode is at least 2 folds more than one in the finishing mode. In general, during the primary mode, CFC might be implemented in a manner of groups selected from a) non-cutting upper section, b) partial-cutting upper section of the hemisphere. As alternative of CFC, one could be also simultaneously cut the upper section of the site by lower frequency of rotation, while the lower section of hemisphere is cut by a higher frequency rotation of cutting, respectively.

The following detailed description is directed to certain specific embodiments of apparatus and method in the present invention. However, the invention can be embodied in a multitude of different ways or designs as defined and covered by the claims. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. Furthermore, embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the inventions herein described.

According the principle discussed above: in the primary cutting mode, one need to avoid or reduce reaming the upper section (zone B) of the hemisphere, while fully reaming the bottom portion, is a major concern of the apparatus design. Reaming entire section of the hemisphere is a purpose of the finishing cutting mode.

The description now turns to the figures. The illustrated example embodiments will be best understood by reference to the figures. The following description is intended only by way of example and simply illustrates certain example embodiment representative of the invention, as claimed.

According to the procedure discussed above, the first preferred embodiment of apparatus dedicates that a structure of the adjustable reamer having a desired spherical cutting radius comprises at least two cutting surfaces, a lower and an upper cutting surfaces. They are arranged in a sequence array and switchable along the longitude axis and have a same spherical cutting radius. Either cutting surfaces could be adjustable in movement toward or away from its fixed counterpart. As FIG. 2 shown, the lower cutting surface is a moveable part and has dynamically enveloped an area defined from pole to intermediate latitude of the hemisphere, while the reamer is rotated. The upper cutting surface has fixed with a frame, which interfaces with the driving shaft. The reamer has two reaming positions: the first position having a first shape wherein the upper surface is partially “hidden” (or partially functioning), and the second position having a second shape: wherein both cutting surface of the reamer are in the working position with a same spherical center and form a hemispherical cutting surface (a second shape).

A First Preferred Embodiment of Apparatus

FIG. 2 has shown a typical case of adjustable reamer. The reamer 10 is, in general, configured by a typically cutting element, a truncated, thin shell in a partial hemispherical form. The cutting element likes one in conventional dome reamer. The lower and upper cutting surfaces are separate-able or switchable along the longitude axis and arranged in a sequence array. The lower cutting surface 32 is statically in a partial spherical shape and has enveloped a first area from pole to intermediate latitude of the hemisphere (zone A). The upper cutting surface 34 is in a partial spherical shape and has enveloped area from intermediate latitude to equator of the hemisphere (zone B). Each cutting surface 32 and 34 has same spherical cutting radius, which corresponds to the desired radius of the hemisphere to be cut. Any design, in which one of the cutting surfaces could be moveable toward and away from its fixed counterpart, is also acceptable. When their spherical cutting centers are merged together on same point at the longitude axis, it forms a full continuous hemispherical cutting surface 90. Each cutting surface here includes a plurality of cutting teeth regularly distributed on its external hollow surface of the shell. Here the detail features of such the hollow surface is not discussed in the present invention, because it is well known as one of the conventional dome reamer disclosed in the prior art.

In particular, the adjustable reamer 10 further comprises following parts: a first base 40, which is integrally attached to internal surface of the hollow, lower cutting surface 32. A second base 60 is a T-shape frame and has one vertically upward branch and two horizontal ends 62, which have integrally fused with internal surface of the hollow upper cutting surface 34. Its vertical branch is a cylinder arm 66, which comprises an interface located at its proximal end. The interface typically comprises two, three or four outward radial posts 48, respectively, in order to engage with a female interface at distal end of the driving shaft (not shown). There are a stepped, through-hole 70 at a center of the cylinder arm 66 along its longitude axis, which includes: a square hole 74 at its lower portion of the hole 70 and a round hole 72 at upper portion of the hole 70.

A connection rod 80 comprises three types of cross sections distributed along its longitudinal axis: a square profile section 83 in a distal portion of rod 80 has a dimension for sliceable fitting into the square hole 74 of the through-hole 70, a first rod section 85 at the middle of rod 80 has a diameter at least 2 mm smaller than one of the round hole 72 and a second rod section 87 at the upper portion of rod 80 has a diameter for sliceable fitting into the round hole 72 of the through-hole 70. So the rod 80 is sliceable within the stepped hole 70, when assembled.

A press spring 82 has an inside diameter engage-able with the first rod section 85 of the connection rod 80 and an outside diameter fit into the round hole 72 of the through-hole 70. The connection rod 80 is a connecting linkage for assembling both the lower and the upper cutting surfaces 32, 34 together in one piece. The connection rod 80 with a spring 82 on the position firstly passes through a center of the hole 70 of the cylinder arm 66, then firmly engages with the first base 40 by its distal end of square section 83 after it passing the square hole 74 of the second base 60 and firmly fixes the lower cutting surface 32 on a position, on which the lower cutting surface 32 is assembled with the upper cutting surface 34 end to end. In that position, the spherical cutting center of the lower cutting surface is equal to the spherical cutting center of the reamer. Since the lower and upper cutting surface merged together, the adjustable reamer forms the full continuous hemispherical cutting surface (seen 90 in FIG. 2). At that position, the spring is in normal (released) condition. This position presents the second shape of the reamer and is referred as an upper end point of the lower cutting surface 32 and defined as the second (fused) position 90 of the reamer 10. If any kind of an external force (from actuating rod of shaft assembly) applied on the proximal end of the connection rod 80, such as actuating mechanism of driving shaft, the lower cutting surface 32 could shift down and space away from the upper cutting surface 34 until a lowest end point (while the spring is pressed) that presents the first shape of the reamer and defined as a first (spaced away) position 92 of the reamer 10 (finishing mode in FIG. 2). At the first position, the first spherical virtual center 96 of the lower cutting surface 32 (it is also the spherical cutting center of the reamer) offsets from the second virtual center 93 of the upper cutting surface 34 by an offset distance 99. At this position 92, the cutting track 87 of the upper cutting surface 34 is far above one 88 while the reamer is in the second position 90. The entire cutting track 95 of the reamer 10 has shown in FIG. 2, which brings about a consequent of less cutting upper portion (at imaginary equator) of the hemisphere.

The offset distance 99 between two virtual centers or points, typically should be at a range from zero to at least 5 mm. At the first position 92, the largest diameter of cross section at an upper portion reamed by the upper cutting surface should be about 2 mm less than the diameter 101 of the imaginary equator (see FIG. 2). So the apparatus accomplishes the primary cutting mode in a manner of partially cutting the upper section of the hemisphere. The offset distance 99 can be continually adjusted by actuating mechanism affiliated with the driving shaft assembly, when the reamer attaches with the assembly.

When the lower and upper cutting surface is merged in the second position 90 (offset distance is zero), the reamer is in a good shape for processing the finishing mode and is able to form the full continuous hemispherical cutting track 97. In order to guarantee that the transition area between two portions or reaming zones of the hemispherical surface are fully covered and smoothly reamed without gap, the lower cutting area (edge) 105 of the upper cutting surface 34 and the higher cutting area (edge) 107 of the lower cutting surface 32 might be partially interlaced or overlapped at their adjacent or transition latitude, such as a manner of a jig-saw pattern or similar.

An alternative configuration or mechanism for adjusting the position of the lower cutting surface 32 to various positions is suitable too. Instead using the press spring 82 paired with the actuating mechanism on the shaft assembly for holding and releasing the position of the lower cutting surface 32 (by moving the first base 40) with a respect to the upper cutting surface 34, any kind of mechanism affiliated with the second base 60, which is able to lock the position of the lower cutting surface 32 along the longitude axis, can also be considered. For instance, to manually adjust the lower cutting surface 32 to the first position 92 and to the second position 90 or multiple positions (not shown), respectively, will allow surgeon to take the reamer out from the site at any point during the primary mode, check status of the cavity and then press the releasing button, manually shift the position of the reamer and relock it while the primary mode is done.

A Second Preferred Embodiment of Apparatus

Instead using the hollow thin-wall (partial) dome as a cutting element forming a cutting surface, according to mechanisms of cutting sphere disclosed in prior art, any other type of the cutting elements are suitable to form either the lower or the upper cutting surface or both, if its dynamic cutting profile is in either partial or full hemispherical form, when the reamer rotates around polar axis of the hemisphere.

For instance, one type of the cutting element disclosed in U.S. Pat. No. 5,755,719 by Frieze and other disclosed in publication of US 20100076442 by Xie could be options for configuring the reamer here. If applied, it brings more advantages to the apparatus and method. Both layers of the cutting surface here can be configured by a same type of those cutting elements mentioned above or a combination from different types.

A combination of the cutting element referred in US 20100076442 as a lower cutting surface and a hollow thin wall partial dome type as the upper cutting surface (shown in FIG. 3), If applied, takes advantages from both types of the cutting element. The typical characteristic of the zone A ha shown that the horizontal radius of the ring varies rapidly from pole to intermediate latitude of the sphere, so a linear cutting speed at the upper edge (at intermediate point) of the offset circular blade is much larger than one at its lower edge (at the pole). Such the difference and friction between bone and blade causes the blade self-turning, while the reamer turns. The self-turning or rotating can significantly reduce the cutting efficiency at area the upper edge of the blade located and bring additional dimension cutting on the polar area, which significantly overcomes the zero cutting speed problems. The final outcome is compromising the effect from difference of the horizontal radius and presents more uniform cutting speed on the entire lower portion. Furthermore, the major advantages of upper cutting surface in hollow thin-wall dome form are the characteristic of its self-centralizing, smooth movement and a function of picking up the debris during reaming.

In a second preferred embodiment of apparatus, there is a major difference from the first embodiment: the reamer 10 has a lower cutting surface, which configured by two circular blades 42. They have symmetrically and pivotally mounted on a branched end of the first base 40 in a manner (the dimension of the blades and arrangement positions) as disclosed in US 20100076442. As shown in FIG. 3, two offset blades 42 configure a lower cutting surface 32 and present a partial spherical, dynamic cutting profile, while it rotated around spherical axis. The upper cutting surface 34 for covering Zone B has configured by a partial spherical hollow dome and remains same as one in the first embodiment. The highest point 107 of the lower cutting surface (upper edge of the blade) has overlapped with the lowest point 105 of the upper cutting surface. In a same manner as disclosed in the first embodiment above, the first base 40, connection rod 80 and second base 60 link the lower cutting surface 32 and the upper cutting surface 34 together. Other structure and functions of the reamer remain same as one disclosed in the first embodiment.

A First Preferred Embodiment of the Method

As shown in a flow chart of FIG. 4, a method of reaming the hemispherical surface with a desired dimension corresponds to the first and second embodiments of apparatus above. The desired dimension means a spherical radius of the surface as surgeon intentional planned, so that the dynamic cutting profile of the reamer used matches the cavity to be cut. The method comprises the steps of:

Step1, providing an adjustable reamer 10 with a desired size of the cutting profile as disclosed above, which is attached to a driving tool (shaft). The preferred driving tool, such as a shaft assembly driven by motor, affiliates actuating mechanism that is able to continually adjust the position of the reamer 10, when they are coupled together. A preferred design of the shaft assembly (not shown) could include an adjustable tongue-like rod concentrically resided on the inside of tube-like driven shaft. There is an actuating means mounted on the handle of the shaft assembly, which engages with the adjustable rod and can manually push down or release up the connection rod 82 through the adjustable tongue-like rod in order to control the position of the lower cutting surface 32 spaced away from or fused to the upper cutting surface 34.

Step 2, inserting the reamer 10 while it is in the second position 90 (a fused position) having the second shape into a target site, or an incision in surgery, while it has a smaller static profile.

Step 3, adjusting the reamer 10 from the second position 90 to the first position 92 (a spaced apart position) having the first shape, here called a first cutting component. The first shape has at least a dynamic spherical cutting surface at least in the partial hemispherical form for covering zone A. So the lower cutting surface is spaced away from the upper one and will present a larger static profile of the reamer 10. At that position, the reamer is ready for performing the primary cutting mode.

Step 4, reaming a bottom (first) portion of the site by rotating the adjustable reamer in the first position 92 with the first shape, until reaching a desired dimension and floor condition, which includes a proper surface quality (size, shape and smoothness) and depth of the site (see cutting track 95 shown in FIG. 2). This reaming step might take most number of times of rotation. The depth usually is approximately equal to the spherical radius to be cut. The surgeon can stop reaming in any stage in order to check the status of the bone condition and avoid overcutting and then re-insert the reamer. When the primary cutting mode is done, the profile of cross section of the cavity shows a typical cutting track 95 in FIGS. 2 and 3. The bottom portion (zone A) of the site is in a perfect partial spherical shape. In some case, the zone B is only partially reamed. The dash line 88 has shown where an imaginary hemisphere profile should be. The cylinder portion of the cutting track 95 has a function of direction guidance when surgeon re-inserts the reamer into the site in correct orientation.

In a robotic operation, the condition check and depth control can be complied by monitor camera or pre-programmed control. It will avoid the inconvenient step of taking the reamer out from the incision during the operation.

Step 5, alternately reaming the site and adjusting the position of the reamer from the first position 92 to the second position 90 until the reamer forms the second shape (a full continuous hemispherical cutting surface), here called a second cutting component. For the case of a robotically operation, both steps could be either simultaneously or alternately carried out by controlling a stepping motor, so progressive reaming will be mush smooth and precise.

Step 6, continues reaming the site while the reamer is in the second position 90 until making sure that the site forms a full continuous hemispherical surface (with a desired dimension, no gap between two zones, see profile 97 in FIG. 2). This step only takes a less number of times of rotations.

Step 7, removing the reamer from the site, while the reamer is in the second position 90.

A Third Preferred Embodiment of Apparatus

Instead the manner of spacing away or merging together two cutting surfaces along the longitude axis (shift up or down), a structure of the adjustable reamer 10 is able to perform the primary mode in a manner without reaming the upper portion of the hemisphere shown in FIG. 5 a. Another type of actuating structure for changing a position/shape of the upper cutting surface 34 could be used to implement the idea of no cutting the upper section of the hemisphere in the primary cutting mode. For instance, the upper cutting surface 34 could be temperately “hidden” or retracted within a “collapsed” position, which is nonfunctioning and has a much smaller cutting profile during the primary cutting mode. During the finishing mode, one progressively expanded the reamer (cutting element(s)) to a second position having the second shape of the reamer (upper cutting surface 34 in functioning), so the reamer has a full dimension of the hemispherical cutting surface.

According to this principle, both types of the blades disclosed both in US 20100076442 and in U.S. Pat. No. 5,755,719 could be more conveniently used to configure an upper cutting surface 34 and be switchable between two positions. As the third preferred embodiment of apparatus shown in FIG. 5 a, regardless the detail of the lower cutting surface 32, a reamer 170 comprises two blades (a preferred one is as disclosed in US 20100076442) for forming the upper cutting surface 34. Each blade 112 pivotally mounted on distal end of a slide-able arm 114. Each arm is slide-able within the tunnel of two horizontal ends 62 of the second base 60 along horizontal direction. So two blades can be retracted or expanded either outwardly or inwardly by either an actuation mechanism of the driving shaft assembly or manually (a preferred mechanism is a gear 175 and rack 176 combination). A detail of dimension of each blade and how properly positioning each blade has disclosed in the US 20100076442 and beyond the coverage of the present invention. Such the movements of the blades are corresponding to the first position (retracted) 192 and second (expanded) position 190 of the reamer 170, respectively. But, the entire cutting surface (a cross section), while the reamer is in the retracted position, could be much smaller than one is in the second position 90 described as the first embodiment, which makes things much easy during steps of inserting the reamer 170 into incision. The reamers can partially or not ream the upper section of the hemisphere while it implements the primary mode. The actuating mechanism for adjusting the positions of the reamer could typically use a gear-rack as driving linkage.

A Fourth Preferred Embodiment of Apparatus

An alternative of the third embodiment of apparatus can also be retracted in other kind of “collapsed” format. A pair of swing-able circular blade configures the second cutting surface, which swings around spherical center on the driving shaft. At its lower position, the pair of the circular blade has formed a cutting surface which overlaps with the fixed (non-adjustable), lower cutting surface formed by another set of cutting elements (such as a semi-circular blade as disclosed in U.S. Pat. No. 5,755,719 by Frieze). The fixed, circular blade here could also be replaced by any other kind of cutting elements discussed above.

The fourth embodiment of the apparatus as shown in FIG. 5 b, the reamer 210 has equipped an upper pair of two circular blades 224 like one as disclosed in US 20100076442. A frame 228 has an upper end and a bottom end for firmly attaching to a lower cutting surface 32, configured by arch-like cutting element 222 following a principle as disclosed in U.S. Pat. No. 5,755,719 by Frieze, The lower cutting surface covers area of Zone A. As shown in FIG. 5 b, there is an interface 226 at the upper end of the frame 228 for coupling with the driving shaft. A pair of swinging-able arms 230 is pivotally mounted on a pivot point (spherical center) of the middle section of the frame by its proximal end. The pivot point is equivalent to the virtual (a sphere center) center 212 of the cutting surfaces and equivalent to the spherical center of hemisphere to be cut. Each blade of the upper pair 224 has pivotally mounted on a distal end of the swinging-able arm 230, so the upper pair 224 of the blade has an arrangement in the orthogonal direction (of 90 degree angle) respect to one of the lower arch-like cutting elements 222. The upper pair 224 of the blade is swinging-able around the virtual center 212 to a first (retracted) position 240 and to a second (expanded) position 242, respectively. A manually mechanism 250 of locking position affiliated with the frame 228 can be used to adjust the arms 230 to the first position 240 and to the second position 242. When the pair of arms 230 are in the first position 240 (swings to its lower end), the upper pair 224 of circular blade and the lower arch-like cutting elements 222 together form a lower cutting surface 32 of the reamer 210, which presents a dynamic hemispherical cutting profile, while the reamer rotating. In the finishing mode, the pair of arms 230 swings up to the second position 242 (swings to its upper end) and the upper pair 224 of blade configures an upper cutting surface 34 of the reamer 210. In the meanwhile, the reamer 210 has a full continuous cutting surface formed by both the lower arch-like cutting elements 222 and upper pair 224 of the blade and presents a dynamic hemispherical cutting profile, while the reamer 210 is rotating. Once again, the dimension and position of upper pair 224 of the circular blade in the reamer 210 has determined by a principle and a method as disclosed in US 20100076442 and is beyond coverage of the present invention.

A Second Preferred Embodiment of the Method

With regarding the third and fourth embodiments of apparatus, the corresponding embodiment of the method should be altered from the first preferred embodiment of the method. Due its smaller profile of the reamer in first (retracted) position 240 of apparatus described in the third and fourth embodiment, the second preferred embodiment of the method is that the step 3) in the first embodiment of the method could be omitted and the step 2) becomes directly inserting the reamer on a target site while it is in the first position. The detail of the steps has shown as a flow chart in FIG. 6.

A Fifth Embodiment of the Apparatus

The fifth preferred embodiment of apparatus dedicates that a structure of the reamer(s) is able to perform the primary mode without reaming the upper section of the hemisphere in other manner. As a fifth preferred embodiment of apparatus, there are two pieces of reamers, a primary reamer and a finishing reamer used for a corresponding primary cutting mode and finishing cutting mode, respectively. The primary reamer with a desired dimension, as the first cutting component here, has a fixed, partial hemispherical cutting surface, which envelopes area (Zone A) from the pole to intermediate latitude of hemisphere as defined above, and is driven by the driving shaft and is able to exclusively ream the lower/bottom portion of the hemisphere. The primary reamer further has a frame with a function for integrally attaching to the cutting surface, such as a thin shell, partial hemispherical dome or others, and directly coupling with the driving shaft for rotation by the interface on its proximal end of the frame. A finishing reamer with a desired dimension, as the second cutting component, has a full continuous hemispherical cutting surface. A typical one likes one of the conventional dome reamer or cutting surface shown dynamical hemispherical cutting profile. Important point is that the cutting surfaces of both reamers should have same spherical cutting radius. The cutting surface here could be configured by any other types of cutting element and setup, which can generate a hemisphere as discussed above and disclosed in U.S. Pat. No. 5,755,719 by Frieze, in publication of US 20100076442 by Xie and others in the prior art.

A Third Preferred Embodiment of the Method

A third preferred embodiment of the method for reaming the hemispherical surface with a desired dimension corresponding to the apparatus described in the fifth embodiment above comprises the steps shown as a flow chart in FIG. 7 of:

-   -   Step A: reaming a bottom (first) portion of a target site by         more frequently rotating a primary reamer (as the first cutting         component) having a first shape around a hemispherical axis,         until the site reaching a desired, partial spherical surface,         floor condition and a proper depth of the site.     -   Step B: reaming an entire surface (second portion) of the target         site by rotating a finishing reamer (as the second cutting         component) having the second shape after step A along same         direction as step A until forming a full continuous         hemispherical surface. This step takes less number of times of         rotation then step A.

A Sixth Preferred Embodiment of Apparatus

As extending the idea of CFC above and opposite from the structure of adjustable reamers disclosed above, the sixth embodiment is related to apparatus, which implements CFC in a manner of applying various cutting frequency (speed) applied on different regions of the hemisphere. A reamer 410 comprises two layers of the cutting surfaces, a lower and upper cutting surface, arranged in sequence along the longitude axis end to end, respectively. As shown in FIG. 8, a cutting element used here is typically of a truncated, hollow thin shell dome, but in a partial hemispherical form with a same spherical cutting diameter. As discussed above, the lower 420 and upper cutting surface 422 correspondingly ream zone A and zone B of the hemisphere, respectively. The two layers of the cutting surface are adjacent in the end to end and form a full hemispherical cutting surface. A first base 440 with a T-shape integrally attached with internal surface of the lower cutting surface by its bottom. A first vertical rod 448 has a first interface 450 at its proximate end for engaging with a first, rod-like driving shaft. A second base 442 with T shape integrally attached with internal surface of the upper cutting surface 422 by its two horizontal ends and has a second vertical arm 449. The second vertical arm 449 has a staged through-hole at its center along the longitude axis and a second interface 452 at its proximal end for engaging with a second, tube-like driving shaft. The through-hole of the second vertical arm 449 has a diameter slide-able fit with the first vertical rod 448. The first vertical rod 448 downwardly passes through the through-hole of the second vertical arm 449, pivotally engages with the second base 442 and connects with the first base 440 by its lower end. Each layer of the cutting surface can couple with a corresponding driving shaft of a shaft assembly and rotate independently in term of a direction and speed of rotation. For example, the second interface 452 corresponding to the upper layer of the cutting surface has coupled with and driven by the tube-like shaft at a relative lower rotating speed and the first interface 450 corresponding to the lower layer of the cutting surface has simultaneously coupled with and driven by the rod-like shaft at a relative higher rotating speed, respectively. The difference of turning speed (frequency) between two cutting layers is at least 2 folds. In general, the cutting surface configured by any type of cutting element is also appropriate for this CFC design.

A Fourth Preferred Embodiment of the Method

A fourth method for preparing a full continuous hemispherical surface with a desired dimension comprising steps of:

-   -   reaming a lower portion of a target site by rotating a first         cutting surface of a reamer around a longitude axis of a         hemisphere at a higher rotating frequency in order that the site         has a desired depth and is at least in a partial hemispherical         form defined from pole to an intermediate latitude of the         hemisphere; and     -   simultaneously reaming an upper portion of the site by rotating         a second cutting surface of the reamer around the longitude axis         at a lower rotating frequency until the site is in a full         continuous hemisphere form, wherein the first and second cutting         surface have an identical spherical cutting radius and rotate         independently in term of a rotating direction and a rotating         frequency thereof, wherein the intermediate latitude locates         between pole and equator of the hemisphere and has a latitude         range defined from 35 to 55 degree while a latitude of pole is         90 degree. The step of reaming the lower portion is implemented         in at least two folds frequency of rotation than the step of         reaming the upper portion implemented.         In Summary, the Methods of CFC could be Implemented in Two         Fashions:

First one: a primary step is cutting the bottom portion of the target site in multiple number times of rotation and postpone cutting upper portion of the site by either retracting the upper cutting surface or shifting the upper cutting surface of the adjustable reamer (in first position) away from spherical center or by a primary reamer. A secondary step is using a reamer having full hemispherical cutting surface to ream entire site to form a full continuous hemispherical surface. The full hemispherical cutting surface here could be an individual reamer (a finishing reamer) or an adjustable reamer with both lower and upper cutting surface that are in a fully functioning position.

Second one: a reamer has both lower and upper cutting surface arranged in end to end fashion to form a full continuous hemispherical cutting surface. The two cutting surfaces adjacent each other simultaneously ream the corresponding portion of the site, but are driven by separated shaft in different cutting speed or direction. The lower one runs in higher rotation speed (frequency) than the upper one in order to compensation the radius difference between the regions.

Multiple variations and modifications are possible in the embodiments of the invention described here, such as any type of cutting elements are applicable to configure a cutting surface of the reamer and any alternative way to assembly a reamer, which are suitable for the methods of reaming the hemispherical surface in various steps discussed in the present invention. Although certain illustrative embodiments of the invention have been shown and described here, a wide range of modifications, changes, and substitutions is contemplated in the foregoing disclosure. While the above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of one or another preferred embodiment thereof. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the foregoing description be construed broadly and understood as being given by way of illustration and example only, the spirit and scope of the invention being limited only by the appended claims. 

What we claim:
 1. A method for preparing a continuous hemispherical surface having a desired dimension comprising steps of: reaming a first portion of a target site by more frequently rotating a first cutting component around a longitude axis of a hemisphere until the site has a desired dimension and is at least in a partial hemispherical form defined from pole to an intermediate latitude of the hemisphere; and reaming a second portion of the site by less frequently rotating a second cutting component around the longitude axis until the site is in a full continuous hemispherical form, wherein the first and the second cutting component have an identical spherical cutting radius, wherein the intermediate latitude locates between pole and equator of the hemisphere and has a range of a latitude defined from 35 to 55 degree while a latitude of pole is 90 degree.
 2. The method of claim 1, wherein the first cutting component is configured by a primary reamer having a fixed, dynamic spherical cutting surface being in the partial hemispherical form and the second cutting component is configured by a finishing reamer having a dynamic spherical cutting surface being in the full hemispherical form.
 3. The method of claim 1, wherein the first cutting component is configured by an adjustable reamer, while the reamer is in a first position with a first shape defining a dynamic spherical cutting surface at least being in the partial hemispherical form, and the second cutting component is configured by the adjustable reamer, while the reamer is in a second position with a second shape defining a dynamic cutting surface being in the full hemispherical form.
 4. The method of claim 1 further comprising a step of adjusting the adjustable reamer from the first position to the second position in order to form the dynamic cutting surface being in the full hemispherical form prior to the step of reaming the second portion.
 5. The method of claim 1, wherein the step of reaming the first portion is implemented by at least twice number of times of rotation than the step of reaming the second portion implemented.
 6. A method for preparing a continuous hemispherical surface having a desired dimension comprising steps of: reaming a lower portion of a target site by rotating a first cutting surface of a reamer around a longitude axis of a hemisphere at a higher rotating frequency in order that the site has a desired depth and is at least in a partial hemispherical form defined from pole to an intermediate latitude of the hemisphere; and simultaneously reaming an upper portion of the site by rotating a second cutting surface of the reamer around the longitude axis at a lower rotating frequency until the site is in a full continuous hemispherical form, wherein the first and the second cutting surface have an identical spherical cutting radius and are rotating independently in term of a rotating direction and a rotating frequency thereof, wherein the intermediate latitude locates between pole and equator of the hemisphere and has a latitude range defined from 35 to 55 degree while a latitude of pole is 90 degree.
 7. The method of claims 1 and 6, wherein the intermediate latitude prefers at 45 degree latitude of the hemisphere.
 8. The method of claim 6, wherein the step of reaming the lower portion is implemented in at least two folds frequency of rotation than the step of reaming the upper portion implemented.
 9. The method of claims 2, 3 and 6, wherein each cutting surface is configured by at least one cutting element, which is able to present a dynamic spherical cutting profile in either the partial or full hemispherical form, while the reamer is rotating around the longitude axis of the hemisphere.
 10. The method of claims 1 and 6, wherein the hemispherical surface is in either concave or convex form. 